1. Field of the Invention
The present invention relates to an interpolation system and, more particularly, to an interpolation system to adaptively perform the interpolation.
2. Related Background Art
In general, an image signal has a large amount of information per unit time and when the image signal is transmitted as a digital signal, a transmission bit rate is extremely high. Therefore, to reduce the transmission bit rate, various kinds of band compression techniques have been proposed. As one of the band compression techniques, there is known a method of reducing the data amount by predictive differential encoding such as DPCM or the like. For instance, a simple predicting method such as an in-field previous value prediction DPCM or the like is an effective method since a relatively large data compression rate is obtained in spite of the fact that it can be easily realized by hardware.
On the other hand, it is also known that code errors occur due to various causes in the case of transmitting the foregoing data through a transmission path. Particularly, in the case where a magnetic recording and reproducing system is the transmission path, large code errors which cannot be error corrected can easily be caused in association with the generation of the signal dropout due to a scratch on a recording medium, choking of the head, or the like. If the error correction cannot be performed, data is generally interpolated by using the correlation of the image. Various kinds of methods have also been proposed with respect to the data interpolation.
With respect to the data interpolation, there is considered a method whereby the optimum interpolation data is calculated by performing the high degree arithmetic operations by using a few pixels before and after the pixel to be interpolated. However, this method is hardly effective in the case where the pixels to be interpolated continuously appear.
On the other hand, in the case of performing predictive encoding and transmitting the data, if one piece of data enters the error uncorrectable state, there will occur what is called error propagation such that errors are caused in all of the data which are decoded on the basis of the error uncorrectable data. Therefore, in many cases, the pixels to be interpolated continue in the horizontal direction of the image.
In the case of unreliable data where the data of the pixels arranged in the horizontal direction continue for the pixels to be interpolated, the interpolation data is formed by using the correlation in the vertical direction of the image. With respect to the interpolation using the correlation in the vertical direction of the image, the substitution by the pixel of the previous line, linear interpolation by the pixels of the lines before and after the line to be interpolated, and the like are considered. However, if the data to be interpolated continuously occur on a plurality of lines, the data cannot be interpolated even by those methods because the substitution or linear interpolation is not possible.